1. School of Metallurgy and Environment, Hunan Province Key Laboratory of Nonferrous Value-Added Metallurgy, Central South University, Changsha, Hunan 410083, P. R. China
2. Hunan ChangYuan LiCo Co., Ltd, Changsha, Hunan 410205, P. R. China
3. Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong, P. R. China